This disclosure is made in the context of LTE to provide the reader a tangible context, but the skilled reader will readily see the analogy with other technologies, where applicable.
The structure of transmission in LTE is organized in frames of 10 ms. One frame consists of ten equally sized subframes. A subframe is either 12 or 14 OFDM symbols, depending on if normal or long cyclic prefix is used. The first symbol(s) in a subframe is control symbols. There can be 1, 2 or 3 control symbols depending need for control signalling. For small bandwidth there can be 2 to 4 symbols, and for some specific cases there is not allowed to have many symbols.
The control signalling can also be done by using PBCH or in the data region as ePDCCH, SIB or dedicated RRM signalling, all these are outside scope of this invention.
The system can be configured with 1, 2 or 4 CRS ports. The CRS are used for channel estimation, synchronization and estimation of channel characteristics. For 1 and 2 CRS ports there are CRSes in 1st, 5th, 8th, and 12th symbol (for normal subframe, non-MBSF and up 2 CRS ports). For 4 CRS ports there are also CRSes in 2nd and 9th symbol. The CRSes in first and second symbol hence share the same time symbols as control signals. The positions in frequency of CRS are every 6th RE per CRS port. CRS port 0 and port 1 share the same symbol but port 1 is shifted three subcarrier compared to port 0, the same goes for port 2 and port 3. Then there is also a shift in subcarrier that depends on cell id of the cell, and the shift is cell id modulo 6.
There are three types of control signals transmitted in the control region, PCFICH, PHICH and PDCCH. The control data is transmitted in one or several Resource Elements Groups (REG). A REG is spread over 4 or 6 REs, but always contain 4 REs carrying payload. A REG is spread over 6 REs in the case there is CRSes in the symbol, the extra REs are reserved for CRS.
The control data is transmitted, for one CRS port, is one modulation symbol per RE. The control data is Alamouti coded when there are 2 or 4 CRS ports. For Alamouti coding two modulation symbols are orthogonally spread over 2 REs. This also holds in LTE for 4 CRS, but here CRS port 0 and CRS port 2 is used in pair, and CRS port 1 and CRS port 3 is used as a second pair.
The existing CRS-IC assistant information is defined for eICIC scenarios from 3GPP specification TS 36.331, v10.5.0. It is defined for CRS-IC in ABS subframe in Rel-11 in 36.331, v. 11.12.0 as:
“neighCellsCRS-Info: This field contains assistance information, concerning the primary frequency, used by the UE to mitigate interference from CRS while performing RRM/RLM/CSI measurement or data demodulation. When the received CRS assistance information is for a cell with CRS colliding with that of the CRS of the cell to measure, the UE may use the CRS assistance information to mitigate CRS interference (as specified in TS 36.101) on the subframes indicated by measSubframePatternPCell, measSubframePatternConfigNeigh, csi-MeasSubframeSet1 if configured, and the CSI subframe set 1 if csi-MeasSubframeSets-r12 is configured. Furthermore, the UE may use CRS assistance information to mitigate CRS interference from the cells in the IE for the demodulation purpose as specified in TS 36.101.”
Further, according to Rel-12, TS 36.331, v. 12.6.0, EUTRAN does not configure neighCellsCRS-Info-r11 if eimta-MainConfigPCell-r12 is configured. This is there stated as:
    “CRS-AssistanceInfoList-r11 ::=SEQUENCE (SIZE (1..maxCellReport)) OFCRS-AssistanceInfo-r11    CRS-AssistanceInfo-r11 ::= SEQUENCE {      physCellId-r11PhysCellId,      antennaPortsCount-r11ENUMERATED {an1, an2, an4, spare1},      mbsfn-SubframeConfigList-r11MBSFN-SubframeConfigList,      ...    }”
Current demodulation and interference suppression methods for control channel region in LTE use the same method for all control symbols. This implies that a full potential for reception may not be used. It is therefore a desire to provide a receiver with improved capability, and to provide an approach which may enhance the systems overall capability.